The present invention relates to an improved method and apparatus for hanging off a coiled tubing (CT) velocity string in an existing production well.
It is well known that liquid loading in gas wells is a problem which results in decreased gas production and in some cases complete cessation of production, i.e., what is known as a "kill". The gas flowing characteristics of a well may be affected by the normal production from gas reservoirs of condensate or water naturally occurring in the formation. If these liquids are not carried to the surface by the gas they will eventually load up in the downhole tubing and cut off the flow of gas. This occurs when there is insufficient transport energy in the gas phase to overcome the head of liquid in the tubing.
By running a line of smaller diameter CT into the existing production tubing string, a reduction in the gas flow area will result in an increased gas flow velocity sufficient to overcome the critical production velocity (C.P.V.). Thus, there has been considerable interest in methods for more economically (both in terms of time and material costs) hanging off the CT in the existing production string, particularly without having to kill the well. (See Wesson and Shursen, "Coiled Tubing Velocity Strings Keep Wells Unloaded," p. 56-60, WORLD OIL (July 1989)).
Current hangoff methods normally involve the following steps:
a. Setting up necessary rigging; PA1 b. Installing a CT hanger/packoff assembly on the existing production string; PA1 c. Installing a pumpout plug into the end of the CT to allow the CT to be run into the well while it is flowing without gas or liquid entering the CT; PA1 d. Running the CT to the desired depth; PA1 e. Energizing the packoff in the hanger/packoff assembly; PA1 f. Installing and setting slips on the CT; PA1 g. Cutting off the excess and removing the CT above the cut; PA1 h. Installing valves and other flow plumbing; PA1 i. Connecting nitrogen source to CT and blowing out the plug in the downhole end of the CT. PA1 j. Disconnecting nitrogen source and placing well on production through the CT velocity string.
Alternatively, if there is a need to initially blow out fluid in the production string, then the CT may be run into the string without the plug, but attached to a nitrogen source. After the nitrogen source is activated and the well fluids blown out, the CT must be retracted and the end plug placed in the CT. This is an extra step requiring additional time and cost.
As may be seen the current methods require the insertion of the downhole end plug which must be pumped out after the CT is run to the desired depth and cut off and this necessitates having a pumpout gas (nitrogen) and delivery system available on site. The method and apparatus of the present invention eliminates this costly and time-consuming step by allowing the operator to "hot tap" the CT which is loaded with gas or liquid after being inserted into the wellbore.